Induction furnace



l ,62 6,485 April 1927' M. UNGER INDUCTIQN FURNACE Filed Feb. 1921 3 Sheets-Sheet 1 Inventor magnus Linger,

Hls Attorney April 26 1927.

M. UNGER INDUCTION FURNACE Filed Feb. 1 1921 3 Sheets-Sheet 2 e mmwww U n n v, wmi

135 His Inve t magnus iern by M His Att ey.

Patented Apr. 26, I927. V

UNITED STATES I 1,626,485 PATENT OFFICE.

MAGNUS UN GER, F PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO- GENERAL ELECTRIC COMPANY, CORPORATION OF NEW YORK.

INDUCTION FURNACE.

Application filed February 16, 1921. Serial "N 0. 445,514.

melting of non-ferrous metals of high conductivity, such, for example, as copper, aluminum and brass.

One of the limitations of electric furnaces of the induction or transformer type is the pinch force,-that is, the compressive electrodynamic force exerted by the magnetic field upon the molten charge when it is carrying currents. At sufliciently high current density this pinch force may interrupt the continuity of the liquid conductor constituting the secondary during the operation of an induction furnace. The current interrupting tendency of. this pinch force may be counteracted by subjecting the molten charge constituting the transformer secondary to a hydraulic pressure, for example, by provid- 'ing a channel located in a vertical plane. The molten charge in this channel, constituting part of the secondary, issubj'ected to the weight of a pool of metal communicating with the upper ends of the channel. In this manner the permissible current density and hence the energy input may be increased. .Nevertheless the pinch force limitation is still a serious factor in the operation of the furnace, and particularly. so when it is desired to melt metal of low resistance such as copper or aluminum.

It is the main object of my present invention further to counteract the pinch force and thereby to increase the permissible power input of induction furnaces. As a result of my invention various other advantages are secured, the efliciency and the power factor of induction furnaces is improved. These advantages are secured by providing an induction furnace with a plurality of channels adapted to contain molten charge and interlinked in parallel with a common magnetic core. Even though the combined sectional area of the separate channels .does not exceed the sectional area of a single channel, the permissible power input of the furnace is increased materially and greater efficiency is secured.

The novel features of my invention will be set forth with greater particularity in the appended claims. For a more detailed explanation of my invention, reference may be had to the following specification taken in connection with the accompanying drawing in which Fig. 1 shows a side elevation of a furnace embodying my invention; Figs. 2, 4, 5, 7 and 9 are sectional views taken in a plane passing through both branches of one of the channels in different modified embodiments of my invention; Fig. 6 is a vertical sectional View of a modification of my invention having a vertical core; Figs. 3 and 10 are vertical sectional views of different forms of furnaces having a horizontal core, the view being taken substantially at right angles to planes in which the channels are located, Fig. 10 being taken on lines l0-10 of Fig. 9; Figs. 8, 11, 12, 13, and 14:, are

horizontal sectional views of different forms of furnaces taken through the primary winding (Fig. 11 being taken on lines 11--l1 of Fig. 9) and Fig. 15 is a somewhat diagrammatic section through the junction of two channels illustrating the circulation of the charge. I

A furnace embodying my invention coinprises essentially a body of refractory material 8 (Figs. 2 and 3) enclosing a chamber 9 adapted to contain a pool 10 of molten charge, the furnace body having adownward extension 11 in which are formed a plurality of open looped channels 12, 13, (see Fig. 3) located side by side on a common winding axis "and communicating at their upper, ends with-the chamber 9. These channe s have been. illustrated 'in Figs. 2 and 3 as having a uniform substantially rectangular section, but they may have sections of various other shapes. In the modification shown in Figs. 2 and 3, these channels surround the middle leg of a horizontal shell type magnetic core 14 on which is located a p'rimar winding 15. Magnetic cores of other esired shape or design may be employed. For example, in Fig. 6, a modifica-' provided operated by a hand wheel 22, or

other suitable means, whereby the furnace may be tilted to pour a charge.

In the modification illustrated by Fig.

as W

thearms-or sections of the channels meet at an acute angle. As shown in Fig. 5, these arms meet at an obtuse angle; in the modification shown i'n'Fig. 4 the channel is round: ed or U-shaped; and in Fig. 9 the channel at the bottom is rounded on one side and angular at the opposite side. Any of these sha es ma be used in a furnace embod in y n my invention.

A circulation of metal occurs in the channels due to several forces, for example, the repulsion between the primary and the secondary, and the mutual electrodynamic attraction between independent conductors carrying current in the same direction. The circulation set up when one or both of these conductors consists of a liquid is illustrated in Fig. 15 which-shows in section the upper ortion of two channels 12, 13', separated y a wall 25, communicating with a pool 10 and carrying currents in the same direction. The magnetic field is indicated by dotted lines surrounding the two channel conductors. Metal in the channels 12', 13 when carrying current is forced toward the adjacent walls or faces of the channels and is thus caused to circulate upwardly into the pool along the inner or adjacent walls of the channels, as indicated by arrows.

Another force caiising circulation is due to an unequal flux density at the bend of the lowermost part of the channels, for example, in a furnace as shown in Fig. 5. Assuming a uniform current density in the metal, the electrodynamic force at the inside of the bond is stronger than at the outside. This causes a circulation as both the current density and the flux densitv at the inner part of the bend are greater than at the outer part and therefore causes the metal to be forced from the inner wall of the bend to the outer wall.

Other forces may be.- superimposed upon these circulatory forces. For example, in some cases the two legs of the channel may be made unsymmetrical to produce a unidirectional thermal circulation.

In Fig. 7 I have illustrated in vertical section a part of a two-channel furnace in which the arm 24 of the channel is of materially smaller cross-section than the arm 25 of the same channel. The adjoining channel is similarly shaped and, as shown in dotted lines, the constricted arm of one channel is opposite the wide arm of the adjoining channel.

Various other modifications maybe introduced in channel outline and section in accordance with the results desired. In Fig. 8 I have illustrated a three-channel furnace in which the channels, 26, 27, 28, are rectangular in sect ion, the longer axis of the sections lying within a vertical plane and extending at right angles to the axis of the primary winding 15. I

In some cases the several channels may to advantage be connected with each other by a conduit. In Figs. 9, 10 and 11, I have illustrated by two sectional views taken at so when one of the channels, or one of the arms of one or more of the channels, is of a different diameter or section than the remaining channels or channel arms. For example, the molten charge may leave the furnace at the mouth of one channel and return through the connecting passage through another channel to the pool.

In the modification shown in Fig. 12, the arms 31, 32, 33, are smaller in cross-section than the arms 34, 35, 36. The fact that the channel arms 31, 32 and 33 are square while the arms 34, 35 and 36 are elongated, in itselt' will tend to produce a circulatory force even when the sectional area of the arms is the same. In the form shown in Fig. 13, both arms of the middle channel '37 are smaller in cross-section than the adjoining arms of the channels 38, 39. Here again the compact shape of the channel 37, which is square in cross-section, as compared with the elongated rectangular cross-section of the outer channels 38, 39, produces a circulatory effect. In Fig. 14, a two channel furnace is shown having the channel arms 40, .41 of lesser square section opposite the channel arms 42, 4-3, or greater rectangular section. As a result both of the difference of crosssection and the ditl'erence of shape and size, a unidirectional circulation of molten charge down the one channel and up another channel occurs.

In all the modifications shown in Figs. 11 to 14 inclusive, a common channel 30. connects the several channels, as best shown in Fig. 10. \Vhen one or more of the channel arms has a greater or lesser cross-section or in shape differs in some respects from the remaining'channel arms so that the current density or flux distribution is unequal, the electro-dynamic force in the channel arms will differ, and unidirectional fiowwill result, accompanied by some incidental local circulation. 4

In a double channel furnace, as above described, the permissible power input is nearly twice as great as in a single channel furnace in which the channel has a sectional area equal to the combined sectional area of the two channels and hence has the same cubical capacity as the two channels combined. This fact is of particular importance when a metal of very'high conductivity is to be melted, as for example, copper or aluminum.

The reason for this greatly increased en- The hydraulic pool level.

szweight of pool material lbs. cu. in.

The pinch force P when rupturing the circuit of this polnt in a single channel furnace at the center of the channel maybe expressed as follows a P= (pounds per sq. in.)

I=current in amperes. Azarea of the single channel in square inches.

Kzconstant (approximately 45x10).

In a double channel furnace this pinch force (7)) for each channel will be expressed as:

p== (pounds per sq. 1n.)

izcurrent in amperes in one channel.

azarea in sq. in. of one channel.

In a one channel furnace the pinch force will open the circuit approximately when I2 f xx In a two channel furnace the pinchforce will, open the circuit approximately when As the furnaces under comparison are assumed to be identical except for the channels it follows that I2 i2 r? Furthermore it has been assumed that A:2a, hence I 'i- KTFE' Therefore I 'Ji'i The total resistance R of the twochannel furnace must be equal to that of the one channel furnace, as the combined cross-' section of the two channels has been assumed to be equal to the cross-section of the single channel. As the current in the single channel furnace is I and the total current in the two channel furnace is 22', the heat generated in the two furnaces under comparison may be expressed as follows:

PR for the single channel furnace' (271) R for the two channel furnace.

As we have found the limiting condition to be 5271:1411, it follows that the power input of the two channel furnace is that is, the power input' in the two chan nel furnace is twice as great as in the onechannel furnace of the same cubical capacity. The energy capacity of a furnace with a greater number of loops will be correspondingly greater.

In a practical furnace the assumed theoretical conditions will be approximated only as the channels are in close inductive rela tion. As this will .to some extent modify the results, nevertheless it is always possible to considerably increase the power input to a furnace by designing it with two or more loops.

The ower factor of a multi-loop furnace is also ound to be greater as the secondary reactance of a multi-loop furnace is lower than for a single channel furnace, the ohmic resistances belng assumed to be equal, as already explained.

What I claim as new and desire to secure by. Letters Patent of the United States, 15 2.-'

1. An electric induction furnace compris.

ing a furnace body providing a main chamber adapted to contain apool, a plurality of open looped channels located side by side on a common winding axis communicating at their ends with said chamber and communicating with each other at their bends, and means for inducing a heating current in a char e contained in said channels.

2. An e ectric, induction furnace comprising a furnace body constituting a chamber adapted to contain a pool and a plurality 0 open looped channels having. a common winding axis and communicatin with said pool, a conduit connectin sai channels at a point removed from sai pool, and inductive means so interlinked with said channels that a current will be induced in a conductive charge in said channels.

3. Ari electric induction furnace compris.

' ing a furnace body constituting a chamber adapted to contain a pool and a plurality of channels, said channels being: bent on themselves and communicating; at their ends with said pool, a conduit connecting said channels at the bends thereoi'. and means for inducing a heating current in said channels.

5. An electric induction furnace comprising a furnace body constituting a chamber and a plurality of looped channels communicating with said chamber, the legs of said channels differing in current-carrying capacity, a conduit connecting said channels adjacent the bends thereof, and means for inducing a current in conductive material 20 contained in said channels.

(5. An electric induction furnace comprising refractory walls providing a reservoir, a plurality of looped channels having a common axis and communicating at their 25 ends with said reservoir, the adjacent legs oi said channels differing in cross-section,

, a conduit connecting said channels at a point removed from said reservoir and means for inductively heating a chargein said chan 30 nels.

In witness whereof, I have hereunto set my hand this 14th day of February, 1921.

MAGNUS UNGER- 

